I am setting up a NetBSD desktop for a friend. Do I have to have
   ghostscript-esp-7.07 installed or can I use the regular GNU
   ghostscript ? The printer (Epson Stylus Photo 820) is supported by
   GIMP Print.

It depends on what you want to do.  If you want to set up CUPS in the
standard way that the CUPS people want you to, and be able to send
Postscript files to the printer and have the be run through
ghostscript and then gimp-print and come out on the printer without
any fuss, then yes, you need to use esp ghostscript, which is just
regular ghostscript with a few changes, mostly I think a raster
interface so that it can be easily connected to gimp-print.

If you set USE_CUPS=YES in /etc/mk.conf, then mk/ghostscript.mk will
automatically choose ESP ghostscript.  If you don't, then you'll get
another kind if you build something else first, and -- I think -- ESP
if you build cups first.  But I can't find the pkgsrc code that makes
ESP be used with cups right now.

So, if you use GNU ghostscript, you'll depart from the way the CUPS
people think things should be, and I suspect that printing PS files on
the Stylus Photo 820 won't work.

-- 
        Greg Troxel <gdt@ir.bbn.com>